The parents of a $8-$yr old boy have agreed to deposit $$5$ in their son's bank account on his $9$th birthday and to double the size of their deposit every year thereafter until his $18$th birthday.

$($a$)$ How much will they have to deposit on his $18$th birthday?

$

$5120$

Incorrect: Your answer is incorrect.

$($b$)$ How much will they have deposited by his $18$th birthday?